In a conventional piston type refrigerating compressor, the compressor is provided with a cylinder block and a cylinder head wherein the cylinder head is mounted to the cylinder block through a valve plate and two gasket elements. The cylinder head is divided into two chambers, such as a suction chamber and a discharge chamber, by an outer peripheral wall portion and an inner partition wall portion. These wall portions are generally equal in length and they are generally parallel to one another and include end surfaces which are disposed in a common plane, the common plane being perpendicular to each wall portion. The end surface of each wall portion is mounted to the valve plate and the gasket element. Hence, a seal is created between the suction and discharge chambers as well as between the suction chamber and between the space external to the cylinder head.
In the above described construction of the compressor, the cylinder head is normally secured to the compressor housing, in contact with the gasket elements and the valve plate, by a plurality of bolts. The bolts are arranged about the perimeter of the cylinder head and extend through the outer wall portions thereof. Therefore, the force pressing the end surface of the outer wall portion to the gasket element is different than the force pressing the end surface of the partition wall portion to the gasket element. Hence, the seal created by the contact between the inner partition wall and the gasket element may not be as consistent as the seal created between the outer wall portion and the gasket element.
Also, the pressure in the suction chamber, which is formed on the outer peripheral portion of the cylinder head, is relatively lower than the pressure in the space external to the compressor. Therefore, a reliable seal must be created between the suction chamber and the space external to the compressor. Further, the pressure in the discharge chamber is higher than the pressure in the suction chamber and, hence, a reliable seal is also needed between these two chambers. However, as mentioned hereinabove, the seal created between the gasket element and the end surface of the partition wall portion may not be as consistent as the seal created between the outer wall portion and the gasket element. Hence, although the seal between the outer wall surface and the gasket element may be reliable, the seal between the inner partition wall portion and the gasket element may not. Thus, the compressed fluid in the discharge chamber may leak through to the suction chamber, resulting in reduced compression efficiency.